The invention concerns a protective casing for optical instruments, in particular a weatherproof protective casing for surveillance systems with video cameras, which has a tubular casing shell with a sealed front wall on one end and backwall on the other end. An instrument support is located within the casing shell rigidly connected to the backwall, and a casing support is located outside the casing shell on its bottom surface, for the attachment of the protective casing in a stationary location. The electrical connections pass through the backwall, and the casing shell can be removed from the backwall and the instrument support.
Such a protective casing is known to the applicant through the trade print script "VIDEO-Security", Edition 3/89, pages 8/9. Protective casings of this type are equipped with the appropriate optical instruments and the corresponding electrical equipment once they have been installed in place by means of a wall bracket, a ceiling hanging or similar attachment. For the purpose of servicing the unit or when repairs have to be carried out, the built-in instruments may have to be disassembled at times. Also changing the optical instruments at a later date are in no way an exception. Since this type of protective casings is preferably used for built-in video cameras, the problems will be explained using a video camera.
When assembled, the casing support, which has the shape of a rail or a sliding carriage, rests on a stationary link head, herein called support. The casing support can be slid in longitudinal direction on this support, and tilted around a horizontal axis, locking in the chosen position.
In the above described known solution the casing backwall is connected to the casing support over a horizontal link axis, and can be tilted, and the instrument support is rigidly connected to this casing backwall. When assembled, the instrument and the casing supports have their longest axes parallel to each other, and the space in-between is occupied by the bottom part of the casing shell, which in order to fulfill its purpose has the shape of a closed tube.
The casing shell can have any cross-sectional form such as square, rectangular, octagonal or round.
For the purpose of disassembly, the casing shell can be slid forward through the gap between the instrument and the casing support, until it reaches a tilt bearing stop. At this point the casing shell remains hanging down in a sloping position due to the effect of gravity. In this position a pendulum movement is possible. Now the instrument support can be tilted up around the back link axis which connects the backwall with the casing support, forming a "V" between the instrument support and the casing support, which however is not stable. The installer now must screw in the camera from the bottom through the instrument support. This is a very difficult, procedure because the individual parts are movable, and the axis of the video camera must coincide exactly with the future position of the casing axis, and must be secured in this position in order to prevent any twisting. In addition, the electrical and electronic parts must be attached to the instrument support and/or the backwall, and finally it must all be wired and connected to the exterior cables. One person can only carry out these procedures with great difficulty.
This is compounded by yet another problem. Video cameras as well as the corresponding lenses come in different shapes and sizes. Lenses can have very different diameters depending on the speed, focal distance and construction. Particularly high speed wide angle lenses have a large diameter, exceeding the measurements of modern video cameras. High speed is required since this type cf camera must also be completely functional in poor lighting conditions.
In order to avoid vignetting in this situation, the optical axis of the lens must be as close as possible in the middle of the casing window, provided, of course, the window is large enough. For the above mentioned reasons it is necessary to install the camera on the instrument support at a determined height, which can vary according to the type of camera or lens chosen. In the past this problem was solved by installing inserts between the camera and the instrument support, but also in this case it had to be secured against twisting and turning. This requirement made the assembly of a video camera difficult and time consuming.
A protective casing is known through DE-GM 86 00 747, in which by means of a pair of lateral grooves an instrument support can be introduced into the hollow space at a single height level. In order to level the different distances between the bottom of the camera and the instrument support, spacers of different thickness must be used, in order to allow the installation of different camera and lens types in the casing at a determined height of the camera axis.
The casing support is made-up of an integral piece consisting of a casing floor with grooves and ribs. A relatively short coupling engages with the grooves, connecting the casing with the tilt bearing. The instrument support and the coupling are not connected through the backwall of the casing, and must be assembled separately. In particular, it is not possible to remove the casing shell from the backwall while the camera remains connected to the backwall, and the latter remains connected to a support or a supporting bracket.